Currently, tens of millions of people are receiving medical treatment of their tissue damages due to accidents or serious organ failures. However, the current surgical treatment or pharmaceutical treatment such as organ transplant cannot be said as a sufficient medical treatment in view of problems of organ supply or the effects of medicine itself, and the like. Thus, many researches have been conducted regarding regeneration of various living tissues which can be transplanted into such patients. Particularly as for the cartilage, it is supposed that there are millions of patients suffering from sports disorders, osteoarthritis or the like only within the country, and thus the development of a technology for enabling producing a cultured cartilage aiming for treating such disorder is strongly desired. The “cultured cartilage” as used herein refers to a 3-dimensional cell combination constituted from cartilage cells.
As regarding the production of a cultured cartilage, there have been reported the production example of a 3-dimensional carrier structure in an artificial environment such as a test tube or incubator by Minas et al., Sittinger, or Naughton et al., Minas et al., Articular Cartilage Defects, 1997, 20 volumes, No. 6, 525-538 pages; International Publication WO 94/20151; International Publication WO 95/3382 1), and the example of in vivo cartilage formation using a scaffold/cell mixture by Vacanti et al. or Naughton et al. (U.S. Patent No. 5,041,138; International Publication WO 90/12603; International Publication WO 97/30662).
In the production of a cultured cartilage, firstly, it is important to secure a scaffold having sufficient functions as a support to which cells are seeded and cultured, and a certain level of mechanical strength. That is, it is required to use a scaffold in which cells can be stably retained and grafted in a uniform distribution state in the culture, preferable proliferation ability and viability can be secured, further fixation treatment such as suture can be carried out in the transplantation into patients after the culture, and the mechanical strength is provided sustainable for (weighted) compression at the initial stage of transplantation.
As approaches thereof, use of various biodegradable plastics has been suggested. Vacanti et al. reported the production of a cultured cartilage using a scaffold obtained by converting a copolymer of glycolic acid and lactic acid (PLGA) to be porous by a salt elution method (U.S. Pat. No. 5,041,138). Moreover, the fore-mentioned Naughton et al. reported the production of a cultured cartilage comprising seeding cartilage cells and culturing them in a scaffold converted to be felt-like by polyglycolic acid, which is one of biodegradable plastics (International Publication WO 97/30662). However, although a certain level of performance can be secured in strength, particularly with the porous scaffold obtained by a salt elution method, there is a problem in grafting ability of cells. And the actual situation is that the cartilage production with a tissue formation in which cells are uniformly distributed similar to living bodies being secured is still in failure. Moreover, the scaffold converted to be felt-like by polyglycolic acid still has problems in grafting ability of cells, thus the situation is similar in failing to form uniform tissues.
As one of solution methods of these, Chen et al. reported the example of cartilage production using a scaffold comprising biodegradable plastic PLGA having the mechanical strength and collagen having cell grafting ability in combination (Chen et al., J. Biomed. Mater. Res., 2000, 51 volumes, 273-279 pages). However, in the actual situation that the safety of collagen itself is in question for such as mad cow disease, the development of the scaffold which does not use collagen as much as possible is desired.
As mentioned above, the porous scaffold using a biodegradable plastic conventionally developed has a problem in grafting ability of cells, and the present condition is that the cartilage production with a tissue formation in which cells are uniformly distributed similar to living bodies being secured is still in failure. Furthermore, for solving such problem, the example of cartilage production using a scaffold comprising collagen has been reported, but there is also a problem in view of the safety of collagen.
In addition, the defective part in cartilage has been pointed out to have problems of invasion of inflammatory cells from the subchondral bone, and formation of fibrous cartilage thereby, thus the cultured cartilage to be developed desirably have performance for preventing invasion of inflammatory cells in the transplantation. For this, as for the 3-dimensional porous scaffold to be used, the contact surface with the subchondral bone desirably has a structure for preventing invasion of inflammatory cells without inhibiting passage of a medium, etc.
Furthermore, the 3-dimensional porous scaffold desirably has characteristics that cells can be efficiently introduced at the stage of cell seeding, and the cells are hard to be leaked after the introduction.